The present invention relates to a stabilized fracturing fluid and to a method of stabilizing a fracturing fluid. More particularly, it is concerned with a stabilized fracturing fluid and with a method of stabilizing a fracturing fluid, which thereby permits smoothly carrying out fracturing operations by preventing a reduction in rheological properties of the fracturing fluid at high temperatures.
In recent years, to increase the production of oil and gas, a fracturing technique has been widely used in which a fluid is injected under high pressure in rock-forming oil and gas layers to break the rock and form cracks therein and, at the same time, a proppant (propping agent) such as coarse sand is introduced to hold or maintain the cracks, thereby accelerating the production of oil and gas.
As a fluid for use in this fracturing, that is, a fracturing fluid, water with a polymer dissolved therein or with a polymer dissolved and cross-linked therein is mainly used. One of the major functions required for the fluid is to have rheological properties that permit cracks to be formed in the reservoir and convey a proppant thereinto. Another function is that a fluid efficiency, that is, leak-off, is small. As polymers for use in the fluid, guar gum and/or derivatives thereof, such as hydroxypropylguar, hydroxyethylguar and carboxymethylguar are mainly used.
Commercial success in the exploration of oil and gas is recently difficult unless the prospecting for oil and gas is conducted in a deeper stratum. For this reason, the temperature of the stratum tends to rise and, in many cases, it reaches 90.degree. C. or more.
At such high temperatures, the guar gum and/or derivatives thereof used in the fracturing fluid are deteriorated or decomposed. This leads to a reduction in rheological properties of the fluid and creates a serious obstacle to the fracturing operation. Accordingly, the inherent functions of the fracturing fluids can be satisfactorily obtained if its rheological properties can be prevented from degradation (e.g., caused by decomposition) even at elevated temperatures.